当开发者创立了自定义组件,并想对该组件增加特定性能时,例如在自定义组件中增加一个点击跳转操作。若间接在组件内嵌入事件办法,将会导致所有引入该自定义组件的中央均减少了该性能。为解决此问题,ArkUI 引入了 @BuilderParam 装璜器,@BuilderParam 用来装璜指向 @Builder 办法的变量,开发者可在初始化自定义组件时对此属性进行赋值,为自定义组件减少特定的性能。该装璜器用于申明任意 UI 形容的一个元素,相似 slot 占位符。
阐明:
从 API version 9 开始,该装璜器反对在 ArkTS 卡片中应用。
装璜器应用阐明
初始化 @BuilderParam 装璜的办法
@BuildParam 装璜的办法只能被自定义构建函数(@Builder 装璜的办法)初始化。
● 应用所属自定义组件的自定义构建函数或者全局的自定义构建函数,在本地初始化 @BuilderParam。
@Builder function GlobalBuilder0() {}@Componentstruct Child { @Builder doNothingBuilder() {}; @BuilderParam aBuilder0: () => void = this.doNothingBuilder; @BuilderParam aBuilder1: () => void = GlobalBuilder0; build(){}}
● 用父组件自定义构建函数初始化子组件 @BuildParam 装璜的办法。
@Componentstruct Child { @Builder componentBuilder() { Text(`Parent builder `) } @BuilderParam aBuilder0: () => void = this.componentBuilder; build() { Column() { this.aBuilder0() } }}@Entry@Componentstruct Parent { @Builder componentBuilder() { Text(`Parent builder `) } build() { Column() { Child({ aBuilder0: this.componentBuilder }) } }}
● 需注意 this 指向正确。
以下示例中,Parent 组件在调用 this.componentBuilder()时,this.label 指向其所属组件,即“Parent”。@Builder componentBuilder()传给子组件 @BuilderParam aBuilder0,在 Child 组件中调用 this.aBuilder0()时,this.label 指向在 Child 的 label,即“Child”。对于 @BuilderParam aBuilder1,在将 this.componentBuilder 传给 aBuilder1 时,调用 bind 绑定了 this,因而其 this.label 指向 Parent 的 label。
阐明:
开发者审慎应用 bind 扭转函数调用的上下文,可能会使 this 指向凌乱。
@Componentstruct Child { @Builder componentBuilder() { Text(`Child builder `) } label: string = `Child` @BuilderParam aBuilder0: () => void = this.componentBuilder; @BuilderParam aBuilder1: () => void = this.componentBuilder; build() { Column() { this.aBuilder0() this.aBuilder1() } }}@Entry@Componentstruct Parent { label: string = `Parent` @Builder componentBuilder() { Text(`${this.label}`) } build() { Column() { this.componentBuilder() Child({ aBuilder0: this.componentBuilder, aBuilder1: this.componentBuilder }) } }}
应用场景
参数初始化组件
@BuilderParam 装璜的办法能够是有参数和无参数的两种模式,需与指向的 @Builder 办法类型匹配。@BuilderParam 装璜的办法类型须要和 @Builder 办法类型统一。
class GlobalBuilderParam { label: string = ""}@Builder function GlobalBuilder1($$ : GlobalBuilderParam) { Text($$.label) .width(400) .height(50) .backgroundColor(Color.Blue)}@Componentstruct Child { @Builder componentBuilder() { Text(`Child builder `) } label: string = 'Child' // 无参数类,指向的componentBuilder也是无参数类型 @BuilderParam aBuilder0: () => void = this.componentBuilder; // 有参数类型,指向的GlobalBuilder1也是有参数类型的办法 @BuilderParam aBuilder1: ($$ : GlobalBuilderParam) => void = this.componentBuilder; build() { Column() { this.aBuilder0() this.aBuilder1({label: 'global Builder label' } ) } }}@Entry@Componentstruct Parent { label: string = 'Parent' @Builder componentBuilder() { Text(`${this.label}`) } build() { Column() { this.componentBuilder() Child({ aBuilder0: this.componentBuilder, aBuilder1: GlobalBuilder1 }) } }}
尾随闭包初始化组件
在自定义组件中应用 @BuilderParam 装璜的属性时也可通过尾随闭包进行初始化。在初始化自定义组件时,组件后紧跟一个大括号“{}”造成尾随闭包场景。
阐明:
此场景下自定义组件内有且仅有一个应用 @BuilderParam 装璜的属性。
开发者能够将尾随闭包内的内容看做 @Builder 装璜的函数传给 @BuilderParam。示例如下:
// xxx.etsclass CustomContainerParam { header: string = '';}@Componentstruct CustomContainer { @Builder componentCloser() { Text(`Custom closer `) } @Prop header: string = ''; @BuilderParam closer: () => void = this.componentCloser; build() { Column() { Text(this.header) .fontSize(30) this.closer() } }}@Builder function specificParam(label1: string, label2: string) { Column() { Text(label1) .fontSize(30) Text(label2) .fontSize(30) }}@Entry@Componentstruct CustomContainerUser { @State text: string = 'header'; param: CustomContainerParam = { header: this.text }; build() { Column() { // 创立CustomContainer,在创立CustomContainer时,通过其后紧跟一个大括号“{}”造成尾随闭包 // 作为传递给子组件CustomContainer @BuilderParam closer: () => void的参数 CustomContainer(this.param) { Column() { specificParam('testA', 'testB') }.backgroundColor(Color.Yellow) .onClick(() => { this.text = 'changeHeader'; }) } } }}